Final answer:
The existence of a taste receptor for fats or lipids is still being debated in the study of gustation.
Step-by-step explanation:
In the study of gustation, or taste, the existence of a sixth taste receptor for fats or lipids is still being debated. While the five primary tastes (sweet, salty, sour, bitter, and umami) have been recognized, recent research suggests that there may be a separate receptor for fats. This hypothesis is supported by studies that indicate different mechanisms and molecular compositions for detecting the taste of fats.